Common variable immunodeficiency (CVID) is characterized by a severe hypogammaglobulinemia. While the clinical picture is dominated by recurrent respiratory and gastrointestinal infections, a subgroup of up to 30% of the patients develops additional autoimmune phenomena, including thrombocytopenia and autoimmune hemolytic anemia. So far no classification allowed a prediction of the coincidence of immunodeficiency and autoimmunity. Here, we propose the size of the peripheral CD19 hi CD21 lo/neg B cell pool as a marker for CVID patients with autoimmune cytopenia and splenomegaly. Interestingly similar B cell populations are also found in patients with SLE and may not only be an epiphenomenon of the disease.